The present invention relates to a color selecting mechanism for use in a cathode-ray tube and its color selecting mechanism frame for fastening and supporting its color selecting electrode thin plate.
As a color selecting mechanism for a color cathode-ray tube, a color selecting mechanism 1 called aperture grill shown in, for example, FIG. 1, has been well known. This color selecting mechanism 1 comprises a rectangular-shaped metallic frame 6 formed of a pair of supporting members 2, 3 opposed to each other and elasticity applying members 4, 5 which are stretched between ends of the supporting members 2, 3, and a mask member or color selecting electrode thin plate 10, which is stretched over a space between the supporting members 2, 3 and contains a plurality of slit-shaped electron beam passage apertures 9 arranged in one direction or in a horizontal direction with respect to a screen.
The color selecting electrode thin plate 10 is made of a metallic thin plate, and contains a number of narrow belt-shaped grid elements 8 which are arranged at a predetermined pitch in the above-mentioned one direction and slit-shaped electron beam passage apertures 9 which are formed between the neighboring grid apertures and elongated in a vertical direction with respect to the screen. As a result, the grid elements 8 are stretched between the supporting members 2, 3 with a predetermined tension by the elasticity applying members 4, 5.
In the color selecting mechanism 1, a damper wire 12 is stretched along the arrangement direction of the grid elements 8 such that it is in contact with a surface of the color selecting electrode thin plate 10, in order to prevent a vibration of the grid element 8.
The aforementioned color selecting mechanism 1 is produced by the following process.
First of all, a spring holder 13 is welded to each of sides of the supporting members 2, 3 and the elasticity applying members 4, 5 of the frame 6. A metallic plate (ordinarily called STC plate) 18 is welded on the bottom face of each of the elasticity applying members 4, 5 so as to produce bimetal effect. Next, the color selecting electrode thin plate 10 is welded between the supporting members 2, 3 of the frame 6 which oppose each other. At this time, in order to apply a predetermined tension to the color selecting electrode thin plate 10, a pressure is applied to the frame 6 before welding, so as to narrow a distance between the supporting members 2 and 3 in the opposing direction (Y direction) (by using a so-called turnbuckle) and with this condition, welding is performed. After welding, the turnbuckle is released so as to allow to apply the predetermined tension to the color selecting electrode thin plate 10.
After the color selecting electrode thin plate 10 is completely stretched, it is passed through a carbon dioxide gas environmental oven so as to be darkened.
Next, damper springs 14 are respectively mounted onto the elasticity applying members 4 and 5 of the frame 6 which oppose each other and the damper wires 12 are stretched between the damper springs 14 which oppose each other. The damper wires 12 suppress the surface of the color selecting electrode thin plate 10 so as to prevent a vibration of the fine grid elements 8. Finally, a spring 15 for fixing the color selecting mechanism 1 to a panel of the cathode-ray tube body is welded to each of the spring holders 13. As a result, assembly of the color selecting mechanism 1 is completed.
In the conventional color selecting mechanism 1, the plane of each of the supporting members 2, 3 of the frame 6 prior to the assembly or a plane 17 on which the color selecting electrode thin plate 10 is to be welded is subject to cutting so as to secure a curved surface (radius of curvature) of a single radius as viewed from the Y direction. The turnbuckle is applied to the frame 6, the color selecting electrode thin plate 10 is stretched, and then darkening processing is performed. In this case, the curved surface of the welded surface 17 of each of the supporting members 2, 3 after darkening is deviated slightly from the single radius due to distribution of the tension in the color selecting electrode thin plate 10 and so on.
However, the radius of an ordinary cathode-ray tube is about 1,000 mm even if it is larger than ordinary sizes. Thus, even if there is any deviation, the plane of the stretched color selecting electrode thin plate 10 draws an outwardly arc across its entire range. As a result, the damper wires 12 are firmly in contact with each of the grid elements 8 thereby preventing a vibration of the grid elements 8 of the color selecting electrode thin plate 10.
Recently, accompanied by a trend in which the screen of the cathode-ray tube has been flattened, the radius of curvature of the plane of the color selecting mechanism 1 has been becoming very large. In a case when the radius of the plane of the supporting members 2, 3 in a frame unit (raw frame 6 before the color selecting electrode thin plate 10 is stretched) of a cathode-ray tube of 66 cm in screen size is a single radius of 15,000 mm, after assembly, the radius of the color selecting mechanism 1, thus the radius of the color selecting electrode thin plate 10 is about 8,000 mm.
As a result of measuring the radius of the plane of this color selecting electrode thin plate 10 in detail, as shown in FIG. 2, it is found that the radius thereof is increased gradually from the center portion toward the end portion in the X direction. In FIG. 2, the axis of abscissa indicates a distance (mm) in the X direction of the screen and the axis of ordinate indicates a distance (mm) in the Z direction assuming that the center of the surface of the supporting members 2, 3 is 0. As evident from FIG. 3, the differential value of this curved line indicates that there are points of inflection a in the vicinity of X=.+-.220 mm. This means that the damper wire 12 is not in contact with the surface of the color selecting electrode thin plate in the vicinity of that point a, thereby indicating that there is no damper wire effective at all.